失明者の脳における視覚系の変化

THE STRUCTURAL CHANGES IN CENTRAL VISUAL SYSTEM IN CASES OF BILATERAL BLINDNESS

I．はじめに

　失明者の脳に起こる視覚系の形態的変化については，Woinow^24）以来，多くの報告があり，特に，19世紀末から20世紀初頭にかけての文献的考察は，Hechst^2）やTsang^23）の論文やPolyak^16）の総説に詳しい。しかし，それらの報告の多くは視神経，視交叉，視索，外側膝状体および視覚領に関するものであり，視蓋前域や上丘まで含めた報告は極めて少ない。

　著者らは，本学脳解剖実習に用いられた人脳の内から，生前に両眼が失明していたことが判明した3例の脳を用いて，その形態学的検索および若干の考察を加えてみた。

The morphological changes in central visual system were studied on 3 cases with bilateral blind-ness.

1. Case 1: A woman, 60-years-old, gave a history of poor vision in both eyes since her childhood. Case2: A 85-years-old woman had a history of weak visual acuity in eyes since 10 years before death. Case3: A 68-years-old man suffered from bilateral amblyopia since completion of the ele-mentary school course.

2. In all cases microscopic examination revealed bilaterally the complete demyelination and the severe atrophy in the optic nerves, chiasm and tracts, except for the right optic nerve and tract of the first case preserving a extremely small amount of uncrossed myelinated fibers.

3. The rostrocaudal length of the lateral geni-culate bodies, calculating from serial Pal-carmine preparations of the case 1, was shortened to about 60% of the control. The magnocellular portion could be fairly subdivided into two layers, but in the parvicellular one its cell and fiber laminations showed marked derangement. Furthermore, the widespread neuron loss was involved in both portions of bilateral external geniculates. No changes could be found in the pregeniculate nucleus.

4. The stripe of Gennari in visual cortex was remained intact in each case. The very slight cytoarchitectural alterations could be recognized in areas 17, 18 and 19.

5. Analyzing the morphological appearance ofnucl. olivaris colliculi superioris (Fuse, '36) in pre-tectal region in the first case, the right side of the nucleus was similar to that of the control, while the left side had a different pattern as shown in Fig. 6. It is the subject for a furture study whether there are any correlations between the anatomical and the clinical findings that in this case only right pupillary reflex had been intact. 6. In the upper layers of the superior colliculus, the neurons within the superficial gray layer were markedly diminished, while considerable amounts of fibers were preserved in the zonal and the optic layer. Some of the later may be considered as the ascending collicular paths to the thalamic nuclei, which hare been concluded from the hodological studies on experimental animals.

7. The thickness of the layers of the superior colliculus and of the central gray substance were measured by means of the construction with several transverse sections through middle portion of the colliculus as shown in Fig. 8. The ratio of each depth of the collicular layer to that of the central gray matter free from any direct retinal connections was estimated. It may be concluded that only superficial layer of the superior colliculus in the long-termed bilateral blindness was clearly collapsed, while in the deeper layers (laminae II and III) no severe changes were pointed out.